The invention relates to an apparatus for treating granular material by drying, film-coating or coating, of the type including a drum which is rotatable about an at least approximately horizontal axis of rotation. The drum is formed with a shell and an end wall portion on either side thereof for containing the material. Inlet and outlet pipes supply a gas, for drying the material, to an immersion body, which has inlet and outlet openings connected to the inlet and outlet pipes. The immersion body is disposed within the drum and assumes a position in which it is immersed in the material.
For the purpose of the invention, granular material will be understood to mean primarily granules and pellets, but also crystalline bodies as are used to make pellets, and the like.
In a known apparatus of the described kind (DE-PS No. 23 15 882), the immersion body has the shape of a ship, its surfaces corresponding to the hull of the ship being provided with inlet openings and its surface corresponding to the deck of the ship being provided with outlet openings for the gas to dry the material. When the drum rotates and consequently the particles of material at the bottom are entrained in the direction of rotation and flow back at the top, this flow of material is divided by the ship-like immersion body and is subjected to the intensive passage of drying gas. However this passage of drying gas reaches only those particles of the material which move past the immersion body or close by it. In a larger drum therefore two or more of such known immersion bodies have to be placed side by side, yet even then considerable amounts of energy are consumed until the material is uniformly dried.
In this known apparatus, if the material is to be coated, a liquid or pulpy medium such as sugar solution or the like is generally sprayed onto the material at a distance in front of the ship-like immersion body. By circulating and drying the material, uniform coatings are then to be formed on the separate particles of the material. The medium serves simultaneously for wetting and for coating, and is consequently tacky, so that it is difficult to prevent particles thereof from settling on the inside walls of the drum and adhering there in regions which fail to or hardly come into contact with the flow of material.